Communication systems may employ data transmission schemes where a sender, on being notified by the receiver of a decoding failure of a transmitted block, schedules a retransmission of the same block of information bits—with identical or modified coding. The receiver retries decoding of the block, improving the chance for successful decoding by combining the previously received data with the retransmitted data.
This combining in the decoder usually involves input in the form of soft decision metric representations of the received bits. Optimum decoding performance requires optimum scaling of these soft decision metrics.
While ideal signal processing preceding a decoder would achieve ideal scaling under all circumstances, it is known that real receiver implementations may suffer to some degree from non-uniform scaling between received soft metrics. In the context of HARQ, such a scaling can be different, e.g. between soft-metrics related to the original transmission of a data block versus those related to a retransmission of the same data bits. The likelihood of scaling differences increases with increasing differences in the processing of the two transmissions in the receiver. A different processing may be performed, for example, for substantially different interference conditions between the two transmissions, where additional processing steps may be activated in order to mitigate an extra interference.
Such a scenario 100 is illustrated in FIG. 1 where a first packet 101a is transmitted from a base station 110 to a mobile station 120 and caused by a non-acknowledgement NACK 105 a retransmission 101b of the first packet 101a is initiated. The original transmission is performed during a first interference scenario 103 while the retransmission is performed during a second interference scenario 104. When the base station 110 receives an acknowledgement ACK 106 a second packet 102 is transmitted.
There is a need to increase the decoding performance of a radio receiver in scenarios of data retransmissions.